Revert "docs: fixes issues with building docs when various components are not enabled."

This causes build problems on OS X. Reverting for 3.7.3 to solve the more general case. We can review this again at a later time.

This reverts commit 8761e9104239f03ba1346ad3ea47a446a81de01a.
cmake: changing where GR_CTRLPORT is defined to properly go into config.h.
cmake: Turning performance counters on at compile-time by default. Still default to off at runtime (modify gnuradio-runtime.conf file to change this).

Experiments showed that this combination adds no overhead to GNU Radio.
Merge branch 'master' into next